Many clinically important antibacterial agents, collectively known as fluoroquinolones, have been discovered. Quinolones which possess a substituted 1,4-dihydro-4-oxo-quinoline-3-carboxylic acid moiety and which have the general structural formula given below are described in J. Med. Chem. 23, 1358 (1980). ##STR1## wherein N may be piperazinyl or the like. Belgian Patent 899399 discloses 1-cyclopropyl-7-piperazinyldihydroquinoline carboxylic acid compounds of the formula ##STR2## wherein R.sub.8 is H or CH.sub.3 and Y is Cl, F or CH.sub.3.
Japanese Patent No. 174367/1983, South African Patent No. 8502369, European Patent Nos. 172651 and 221463, 119087, U.S. Pat. No. 4,556,658, 1985 and J. Med. Chem. 1990, 33 (1645-1656), disclose compounds represented by the following general formula having an amino group at position 5. ##STR3## wherein R.sub.1 is ethyl, cyclopropyl; X is CH, CF, C--CH.sub.3 ; and N is piperazinyl or the like.
The 7- (3-aminopyrrolidinyl) quinolones which are represented by general formula given below: ##STR4## wherein X is N, CH or CF; R.sub.1 is ethyl, cyclopropyl, 2,4-difluorophenyl or 4-fluorophenyl; R.sub.9 is NH.sub.2, CH.sub.2 NH.sub.2, pyrrole, imidazole or pyrrolidine group and R.sub.10 is --OCH.sub.3, CH.sub.3, C.sub.6 H.sub.5 or .dbd.CH.sub.2 are disclosed in J. Med. Chem. 1988, 31 (1598-1611); J. Med. Chem. 1990, 33 (849-854); EP 347851, EP 362759, Abstracts of the 30th Interscience Conference on Antimicrobial Agents and Chemotherapy, Atlanta, Oct. 21-24, 1990, Abstract No. 395.
Some of the above disclosed compounds are clinically useful. However, there exists a continuing need to develop new antibacterial agents because the effectiveness of existing antibacterial agents diminish as strains of pathogens develop resistance. In addition, certain antibiotics exhibit unsuitable pharmaceutical properties and exert serious adverse side effects in humans.